Yep, it's fair to say that good things really do come in threes. And for the Pond's penultimate adventure, it seemed only fitting that we slowed things down to explore the impact The Doctor's had on their life, and - surprisingly - them on his.

For the most part, The Power of Three hit every emotional beat with satisfying eloquence, and succeeded in delivering a fitting epitaph to the TARDIS trio. Whether the episode as a coherent whole was up to scratch though, isn't quite as clear.

The set-up was as brief as it was intriguing - one day, out of absolutely nowhere, thousands of tiny, shiny black cubes started popping up all the globe. While the world and the Doctor flew straight into Defcon 5, the cubes responded by doing the last thing anyone expected - absolutely nothing.

So began the 'Year of the Slow Invasion', and an episode in which we (and more importantly, the Doctor) were able to see what Amy and Rory get up to during their non-planet hopping downtime. Inevitably, when the cubes finally did make their nefarious plans known, no-one was expecting it.

For a good three quarters of its running time, The Power of Three was slightly brilliant.

By focusing on the relative mundanity of Amy and Rory's 'other' life, it succeeded in paying off this season's subtle shift away from the Ponds' reliance on the Doctor. Whether hanging out with friends, going to jobs they loved, or simply chilling out in bed together, it sold the idea that the Ponds are finally ready for a normal life.

In fact, it was the Doctor's counter reaction that gave the episode its heart. His big sell to Amy on travelling the universe, and the revelation that he's not running away from, but to life's smaller moments was heartwarmingly poetic.

It also had humour galore, with Russell T Davies-style celebrity cameos, irreverent silliness (giving the Doctor OCD on a galactic level made perfect, amusing sense), and - of course - the return of the best companion the Doctor never had, one Brian 'Diligence' Pond.

Who needs Oswin when you have a man who can spend four days sat in the TARDIS without a toilet break?

The cubes meanwhile were as beguiling in motive as they were design, and when they finally struck, the terror of a planet-wide collective myocardial infarction (I've been watching a lot of Scrubs recently) was genuinely, erm, heart-stopping.

It was only the rushed resolution that failed to deliver.

While the concept of an intergalactic pest exterminator seeding sexy slug pellet cubes all over the world was nifty, the introduction of the maskless Darth Vader-ish Big Bad behind them seemed a pointless afterthought.

Not only did he arrive too late in the tale to really feel threatening, but some of his motives seemed bizarre, too - what was the point of the Q*Bert-mouthed orderlies? And why were they bringing anyone back to the ship in the first place?

Equally, the Doctor's magic wand wave-away of the world's mass heart attack felt frivolously easy considering the initial impact (and is anyone else worried about the more-than-likely vegetative state of the millions of people who have just come back to life - after around ten minutes sans oxygen?).

While The Power of Three had its problems, the simplicity of its driving plot and the focus on character delivered.

Whatever happens in next week's final Pond adventure, at least this will serve as fitting coda to one of the most memorable Doctor/Companion(s) pairings so far.